Stock-Based Compensation Expenses (Details) (USD $)	3 Months Ended		6 Months Ended
	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2015	Jan. 31, 2014	Jul. 31, 2014
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 1,061,000	$ 1,069,000	$ 2,398,000	$ 2,016,000
Estimated income tax benefit	(383,000)	(403,000)	(851,000)	(749,000)
Net stock-based compensation expense	678,000	666,000	1,547,000	1,267,000
Total remaining unrecognized compensation cost related to the unvested stock-based awards	9,923,000		9,923,000
Estimated forfeitures related to unvested stock-based awards	821,000		821,000
Weighted average number of years net compensation cost is expected to be recognized over			3 years 1 month 6 days
Stock-based compensation capitalized and included in ending inventory	68,000		68,000		68,000
Stock Options
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	731,000	719,000	1,489,000	1,367,000
Performance Shares
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	167,000	230,000	575,000	407,000
Employee Stock Purchase Plan - ESPP
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	53,000	43,000	106,000	88,000
Discount offered to employees participating in the ESPP as a percentage of market price			15.00%	15.00%
RSUs and restricted stock
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	96,000	68,000	200,000	136,000
Share units
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	14,000	6,000	28,000	12,000
Total equity-classified stock-based awards
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	1,061,000	1,066,000	2,398,000	2,010,000
SARs
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	0	3,000	0	6,000
Cost of sales
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	66,000	84,000	133,000	137,000
Selling, general and administrative expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	856,000	832,000	1,958,000	1,603,000
Research and development expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 139,000	$ 153,000	$ 307,000	$ 276,000